Process and apparatus for synthetic packaging

ABSTRACT

In order to improve a process for producing plastic packaging, particularly using plastic sheets, lateral sections (14) projecting beyond goods to be packaged being at least partly shrunk by heat supply, so that heat-sensitive goods also can be packaged in an economical and visually attractive way, it is proposed that the heat supply be interrupted as soon as the shrinking process starts in an area of plastic packaging subjected to heat, and that mechanical pressure be exerted on the heated areas of plastic immediately afterwards. An apparatus for carrying out the process for producing plastic packaging has an uptake area, a heat supply device and pressure members (15).

The present invention concerns a process for producing syntheticpackaging, in particular by using sheets made of synthetic material,synthetic material projecting in areas of lateral edges of the goods tobe packaged being heat-shrunk by means of heat supply. Further, thepresent invention concerns an apparatus for carrying out a process forproducing plastic packaging.

Examples of methods and apparatus reflecting background art aredisclosed in, inter alia, WO 84/03872 and DE-A-1 778 422.

Shrink synthetic packaging and processes for producing such shrinksynthetic packaging are known in the state of the art. Sheets to beshrunk, using heat supply, around goods to be packaged, are placedaround these goods or bundles and are shrunk in projecting lateralareas, which results in tight packaging. For this, only specific shrinksheets are used. A disadvantage of the known process is that thepackaging is not suitable for all goods, especially not forheat-sensitive goods which deteriorate because of heat supply or,because of their sensitivity to heat, undergo a change in texture,melting or the like. Moreover, shrink packaging is not suitable forpackaging having a large surface and produces a packaging edge whichcannot be visually reproduced. The sheets shrink in an uncontrolledmanner in areas which have heat applied to them, and partly produce veryunpresentable edge areas. Finally, all known shrink-sheet packagingprocesses are not always economically applicable because of the timeneeded for complete shrinking.

Futhermore, it is known for sensitive goods also to be packaged insynthetic sheets which are stuck together.

Based on this state of the art, the present invention is aimed atimproving a process for producing synthetic packaging of this type,which can be used on heat-sensitive goods and which can be used onextensive packaging areas, while producing a visually attractive andpartly reproducible packaging edge.

This aim is achieved by the process and apparatus according to theappended claims. To achieve this aim, it is proposed by the presentinvention that heat supply be interrupted as soon as a shrinking processbegins in a given area of synthetic packaging subjected to heat and thatmechanical pressure be applied to heated areas of synthetic packagingimmediately afterwards.

Using a process in accordance with the present invention, correspondingareas of synthetic packaging are not subjected to heat until they arefully shrunk, instead only until shrinking has just begun. This momentis not to be exactly mathematically recorded, instead it is a moment atwhich parts of the synthetic packaging begin to shrink while other partshave become soft because of the heat supplied. At this moment,mechanical pressure is exerted on the heated areas so that the partsmelted or softened by heat supply join together in a flat form. Apackaging edge produce in this way offers, in terms of packaging,sufficient mechanical holding, without as much heat needing to besupplied as may adversely affect heat-sensitive goods.

The present invention enables the use of synthetic packaging in general,which does not necessarily have to involve particular shrink sheets of aconventional type. A process in accordance with the present inventioncan also be used on heat-sensitive goods, as these are not subjected toheat.

An important field of use is the packaging of plastic items. It isknown, for example, for plastic waste bags, in a rolled-up form, usedalso for congealing and frozen materials and the like, to be soldpackaged such that the bundle rolls cannot be unrolled. For marketingreasons, it is desirable to use, for example, presentably printedplastic sheets to package such bundles. If conventional shrink sheetsshould be shrunk on in the lateral areas by a corresponding heat supply,bags in such bundles would simultaneously also be melted, whereby thesewould acquire at least an unattractive exterior. Such bundles can bepackaged, in a visually attractive form, in plastic sheets, using aprocess in accordance with the present invention, also without the useof particular shrink sheets. This naturally also applies to otherheat-sensitive items, whether they be plastic, paper, foodstuffs or thelike.

According to a favourable aspect of the present invention, control ofinterruption of the heat supply and exertion of mechanical pressure iscarried out dependent on time. Depending on the goods to be packaged andthe synthetic material used to make the packaging, a given moment forinterrupting the heat supply and application of mechanical pressure caneasily be empirically recorded.

Alternatively, or additionally, it is possible to apply heat to acontrol sheet aligned parallel to a bundle to be packaged and todetermine the right moment for interruption of the heat supply by meansof optical or temperature sensors.

In one aspect of the present invention, the heat supply is effected bysupplying hot air. This confers the advantage that the heat is targetedand can be supplied exactly in terms of time as, when the hot-air supplyis interrupted, there is automatically an immediate interruption of heatsupply.

In an advantageous aspect of the present invention, the application ofmechanical pressure occurs in the direction of the goods to be packaged.The heated areas are thereby pressurised in the direction of the goodsto be packaged and adhere or melt there, which results in a straight,flat synthetic surface having a good mechanical consistency and lying onthe packaged product.

In a favourable way, flat pressure devices are used to exert mechanicalpressure. In a further favourable aspect of the present invention, thepressure devices can be cooled during or immediately after applicationof mechanical pressure. Supply of cool air is favourably suitable forthis.

Polypropylene material is, for example, an alternative to other knownshrink sheets, as synthetic material for producing plastic packaging.

The process according to the present invention enables, in a simple andeconomic way, production of visually attractive plastic packaging, inparticular also for heat-sensitive goods.

According to the present invention, an apparatus for carrying out theinventive process is also specified, which, in its main structure, hasan uptake area for a product to be packaged wrapped in a plastic sheet,a heat-supply device directed to relevant areas, and pressure membersfor exerting mechanical pressure on corresponding areas of the productto be packaged. The heat-supply device favourably comprises hot-airblowers. The pressure members are, in a favourable aspect of the presentinvention, pressure plates, which can pivot advantageously in thedirection of the product to be packaged. Consequently, mechanicalpressure can be exerted on relevant areas by means of the apparatusconcerned after the supply of hot air, such that said pressure platesare pivoted onto the product to be packaged and thereby compress theareas of heated plastic. The apparatus moreover has a cooling device forsaid pressure plates, advantageously a cool-air blower.

According to the present invention, a process and an apparatus areproposed, which enable economical packaging also of heat-sensitive goodsin a visually attractive form by means of shrinkage of syntheticwrapping materials.

Further advantages and characteristic features of the present inventionare illustrated by the following description, with reference to theaccompanying drawings, in which:

FIG. 1 is a schematic, perspective view of an embodiment of a packagingapparatus;

FIG. 2 is a partly sectioned view of an apparatus in FIG. 1, and

FIGS. 3a-3f are schematic views of an embodiment of a packaging process.

A packaging apparatus shown schematically in FIGS. 1 and 2 is disposedin a housing which, for reasons of simplification, is shown by two sidewalls 2. These side walls 2 serve to house shafts and rollers, forexample, a return roller 10 for a feed band 3. The feed band 3 can becombined, in a known way, with conventional rolling-up devices, in orderto wrap goods in a surrounding package. The wrapped packaged goods canbe moved forward on rollers 4 by means of the feed band 3, where theproduct wrapped in plastic packaging material is briefly held. Atspecific points, the packaging material is subjected to hot-air suppliedby hot air blowers 5. A controlling means which is not shown providesfor interruption of the hot-air supply at a suitable moment. Pressureplates 7 are disposed to be able to pivot on a cross-piece 6, forexample by means of a rotating cylinder. For reasons of clarity, onlyone pressure plate 7 is shown in FIG. 1, nevertheless the packagingapparatus 1 concerned is symmetrically designed. The pressure plate 7can be pivoted about an axis 8 to an upper position shown in FIG. 1 orto a lower position as shown in FIG. 2. The pressure plate 7 is designedon its free edge, such that it can be pivoted between rollers 4. Inorder to make the position of the pressure plate 7 and its pivoting axis8 variable, the rotating cylinder 9 can be released, such that thepressure plate 7 can be shifted on the cross-piece 6.

The packaging process is illustrated in FIGS. 3a-3f. For example, a rollof bags 11 is shown in FIG. 3a. This comprises rolled-up plastic bagswhich are to be sold for holding waste material. A packaging sheet 12 isshown in FIG. 3b. The roll of plastic bags 11 is wrapped in thispackaging sheet 12, which results in the bundle as shown in FIG. 3c. Therim of the roll of bags is indicated by a dashed line 13, whereby thepackaging sheet 12 develops projecting material 14 on both sides. Hotair is targeted on these projecting sides 14, such that a softening orshrinking process is started. Then the state as shown in FIGS. 3d and 3earises, in which the projecting side material is softened, as a resultof being subjected to heat, and begins to shrink. At this moment, asshown in FIG. 3f, pressure is exerted on said side material by means ofpressure plates 7, in the direction of an arrow 15, which results in aflat, orderly packaging lateral edge. Through cooling of the pressureplates 7, the transmitted heat can be removed and the cooling of saidpackaging lateral edge can be accelerated. A cooling device 16 can bedisposed, for example, above the cross-piece 6, such that cool air isdirected onto the pressure plates 7 pivoted upwards.

The embodiments illustrated in the accompanying drawings are shown onlyby way of illustration and are not limiting.

I claim:
 1. Process for producing plastic packaging, comprising:coveringgoods to be packaged with a sheet of synthetic material, such thatsections of side areas of the synthetic material project beyond thegoods to be packaged at two opposite sides of the goods to be packaged,supplying heat to each section until the section is at least partlyshrunk by the supplied heat, interrupting the heat supply as soon as theheated section begins to shrink in areas subjected to heat, andimmediately afterwards exerting mechanical pressure on the areas of theheated section subjected to heat.
 2. Process in accordance with claim 1,wherein interruption of the heat supply and exertion of the mechanicalpressure are controlled dependent upon time.
 3. Process in accordancewith claim 1, wherein a time for interruption of the heat supply andexertion of the mechanical pressure is determined by subjecting areference control sheet to heat and measuring a response of thereference control sheet.
 4. Process in accordance with claim 1, whereintemperature sensors are used to determine a time for interruption of theheat supply and exertion of the mechanical pressure.
 5. Process inaccordance with claim 1, wherein hot air is used to supply heat. 6.Process in accordance with claim 1, wherein the mechanical pressure isexerted in a direction toward the goods to be packaged.
 7. Process inaccordance with claim 1, wherein substantially flat pressure devices areused to exert the mechanical pressure.
 8. Process in accordance withclaim 7, wherein said pressure devices are cooled.
 9. Process inaccordance with claim 8, wherein cool air is used to cool said pressuredevices.
 10. Process in accordance with claim 1, wherein the syntheticmaterial is polypropylene.
 11. Apparatus for producing plasticpackaging, comprising:an uptake area for holding a product packed insynthetic material to be packaged, a heat-supply device for supplyingheat to each section of the synthetic material that projects beyond oneof two opposite sides of the product to be packaged and for interruptingthe supplied heat when the heated section begins to shrink in areassubjected to the supplied heat, and pressure members for exertingmechanical pressure on the heated section of the synthetic materialimmediately after the supplied heat is interrupted.
 12. Apparatus inaccordance with claim 11, wherein said heat-supply device includes hotair blowers.
 13. Apparatus in accordance with claim 11, wherein saidpressure members are formed of pressure plates.
 14. Apparatus inaccordance with claim 13, wherein said pressure plates are pivotable.15. Apparatus in accordance with claim 11, wherein a cooling device isemployed to cool said pressure members.
 16. Apparatus in accordance withclaim 15, wherein said cooling device includes a cool air blower.